1. Field of the Invention
This invention relates to devices commonly referred to as nutrunners used in manufacturing for applying and securing nuts to bolts during assembly operations. More particularly, this invention relates to improvements in control circuitry for electrically operated nutrunner devices.
2. Description of the Prior Art
Electric nutrunner systems have generally employed a motor having means mounted thereto for engaging a nut and turning it onto a bolt. The system objective being to not only attach the nut quickly to the bolt but to secure the nut with a desired torque. During this sequence the rotational velocity of the nut and the applied torque changes rapidly and therefor it requires an accurate control system to obtain reliable results under the varying conditions encountered in manufacturing facilities.
Heretofore digital systems have been employed using well known digital sampling techniques. A torque is applied to the nut by means of an electric motor and maintained constant until the nut begins to tighten. The applied torque is periodically monitored and when the sampled torque reaches a predetermined level, indicating that the nut is tight, the applied torque is removed.
In such a digital system, during the short time interval occurring between the moment when the nut becomes tight and the moment the torque is removed, the tension on the bolt and the tightness of the nut changes dramatically. Since such changes occur at a rate much faster than conventional sampling circuitry can accurately respond, the selected desired tightness is often exceeded before the applied torque is again measured. This problem is often compounded when the system displays the last sampled applied torque as the actual finished condition, even though the inaccurate system yielded a much higher torque.